Due to their rigid construction and high reliability, impedance position sensors are often used to determine the position of an object in harsh environments. This is particularly true in aircraft, where such sensors are used to determine the position of the aircraft's flight surfaces or landing gear, etc. A typical impedance sensor includes a plurality of serially connected coils wound coaxially on a nonmagnetic bobbin. A target element, coupled to the object whose position is to be sensed, moves within the coils and changes the coils' impedance. This change of impedance can be measured to give an indication of the position of the object.
The problem faced by electrical engineers who design impedance position sensors is to determine the number of turns of wire that each of the plurality of coils should contain so that the impedance of the sensor varies according to a desired impedance function as the target is moved within the coil. Most often, it is desirable to have the impedance vary linearly as the position of the target is changed. However, sometimes it is desirable to have a sensor with an impedance that varies in a nonlinear fashion. In the past, engineers would design such sensors by winding an equal number of turns on each coil and plotting the change in impedance versus the target position on a graph. The number of turns in each coil would then be manually adjusted so that the impedance of the sensor varied as closely as possible according to the desired response of the sensor. Because the total impedance of the sensor varies according to the self inductance of each coil and the mutual inductance coupling between the coils, this process of manually adjusting the number of turns in each coil so that the impedance varies according to the desired response becomes nearly impossible as the number of coils increases. Specifically, because changing the number of turns in one coil affects the inductance of each of the other coils, it becomes nearly impossible to find the number of turns each coil should have so that the total impedance of the sensor varies as desired. In prior art inductive position sensors, it was very difficult to develop a sensor design having an inductance that did not vary from the desired inductance function by less than 0.25 percent.
Therefore, to overcome the problems of prior art impedance sensor design, what is needed is a method of designing position sensors that is quick, easy and accurate.